We propose to study the immune mechanism of defensins in host resistance to human HIV-1 and related retroviruses of non-human primates. Our long-term objectives are: 1) to identify innate immune system molecules involved in the pathogenesis of HTV-1 infections in primates. 2) to characterize the carbohydrate-binding specificity of theta- and alpha-defensins, and to correlate this property with their activity against HIV-1. 3) to identify potent theta-defensins for future in vivo studies designed to assess their therapeutic usefulness. No in vivo studies are proposed hi this grant. Theta-defensins are cyclic octadecapeptides expressed by leukocytes of Old World monkeys and some other non human primates. Their ability to recognize certain carbohydrate structures (glycans) allows some 9-defensins to bind both gp120 of HIV-1 and CD4 with high affinity, and to prevent the entry of R5 and X4 strains of HIV-1 into otherwise susceptible human cells. At least 6 0-defensin genes exist in the human genome, and theta-defensin mRNA exists in human bone marrow, thymus, and spleen. However, human theta-defensin genes and their mRNA contain a premature stop codon, and human cells do not produce theta-defensin peptides. Retrocyclins 1-3 are synthetic peptides that represent the theta-defensins that humans could produce if the silencing mutation (the premature stop codon) were absent. Retrocyclin-2 is effective against HIV-1 primary isolates representing subtypes A,B,C and CRF01_AE, which cause most HIV-1 infections worldwide. Because retrocyclins are noncytotoxic and noninjurious to vaginal lactobacilli, they provide intriguing lead compounds for future pharmaceutical development. The studies contained in this proposal are intended to provide a knowledge-platform that will facilitate the development of therapeutic theta-defensins in the future. The specific aims are: 1). To synthesize novel theta-defensins, including peptides based on theta-defensin gene sequences in non-human primates and analogues of human retrocyclins, and to test them for activity against HIV-1 and cytotoxicity. 2). To identify the sugars and oligosaccharides that primate theta-defensins bind, and correlate binding with their antiretroviral properties. Aim 1 will be accomplished by solid phase peptide synthesis and in vitro protection assays using peripheral blood mononuclear cells and indicator cell lines. Specific Aim 2 will be realized by a combination of microchemical techniques, including surface plasmon resonance, tandem mass spectrometry, and state-of-the-art lectinomic and peptidomic chemistry.